1. Field of the Invention
The present invention relates to wireless IC devices.
In particular, the present invention relates to a wireless IC device used in an RFID (radio frequency identification) system and to an electromagnetic coupling module included in the wireless IC device.
2. Description of the Related Art
An RFID system has been developed and used as an article management system. The RFID system includes a reader/writer that generates an induction field and communicates in a non-contact manner with an IC tag (also referred to as a wireless IC device) which stores specific information and is attached to an article. Thus, information is transmitted between the reader/writer and the IC tag. A wireless IC device used in such an RFID system is disclosed in PCT International Publication WO2009/081719. As illustrated in FIG. 11A, a wireless IC device includes two inductance elements L1 and L2 (helically connected coil conductors) that are electrically connected to a wireless IC chip 10 and electromagnetically coupled to radiation plates 30A and 30B.
However, in the above-described wireless IC device, coil conductors on the bottom layer which face the radiation plates 30A and 30B are arranged in the vicinity of connection points to the wireless IC chip 10 having a high impedance, as illustrated in FIG. 11B. Such arrangement increases the impedance of the inductance elements L1 and L2, which makes it difficult to ensure impedance matching between the wireless IC chip 10 and the radiation plates 30A and 30B. In FIG. 11B, the connection point X of the inductance elements L1 and L2 serves as a virtual ground.